Question

A gaseous compound having carbon, hydrogen and oxygen was burnt in the presence of oxygen. After combustion, 1 volume of the gaseous compound produces 2 volumes of $\text{C}{{\text{O}}_{\text{2}}}$ and 2 volumes of steam. Determines the molecular formula of the compound, if all the volume were measured under the same conditions of pressure and temperature.
a.) ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{{\text{O}}_{\text{2}}}$
b.) ${{\text{C}}_{\text{3}}}{{\text{H}}_{\text{6}}}{{\text{O}}_{\text{3}}}$
c.) ${{\text{C}}_{\text{4}}}{{\text{H}}_{\text{8}}}{{\text{O}}_{\text{2}}}$
d.) ${{\text{C}}_{\text{5}}}{{\text{H}}_{\text{10}}}{{\text{O}}_{\text{3}}}$

Answer 1

We can solve this problem by writing the chemical reaction in an assumption and balance the chemical reaction. After balancing, then compare the number of atoms in the left hand side and right hand side.

Complete step by step answer:
Let us assume the number of carbons in the compound be x, the number of hydrogen in the compound by y and number of oxygen in the compound be z. When we are writing the chemical reaction:
${{C}_{x}}{{H}_{y}}{{O}_{z}}+2{{O}_{2}}\to 2C{{O}_{2}}+2{{H}_{2}}O$
According to this reaction, one volume of the gaseous compound produces two volumes of carbon dioxide and two volumes of steam.
After balancing the reaction, compare the number of atoms in the left hand side and right hand side.
So, x = 2
y = 4
(z + 4) = 6, z = 2
So, the molecular formula will be${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{4}}}{{\text{O}}_{\text{2}}}$.
So, the correct answer is “Option A”.

Note: Here, the reaction takes place as a combustion reaction. In the combustion reaction, hydrocarbons break down into carbon dioxide and water. The essential condition for the combustion is the presence of oxygen is must. In the absence of sufficient oxygen, partial combustion will take place.